58 research outputs found
DĂ©fluoruration des eaux d'exhaure de Youssoufia (Maroc) par percolation sur les cendres volantes de charbon
Dans cette étude, nous nous sommes intéressés à la défluoruration des eaux souterraines de Youssoufia (eaux d’exhaure) par percolation en colonne sur les cendres volantes de la centrale thermique d’El Jadida et à la désorption des fluorures par la suite. Les résultats obtenus ont montré que :- le rendement d'élimination du F- est d'environ 97 % dans nos conditions expérimentales avec un temps de séjour supérieur à 72 heures ;- la régénération des cendres est possible à l’aide de NaOH;- le nombre de cycles successifs tolérés par les cendres permettant d’atteindre des efficacités convenables est d’au moins huit.The layer of black phosphate in Youssoufia is characterized by the presence of underground water in the building sites. This drainage water must be removed to allow the exploitation of these layers. Observations of the tonnage/flow relationship during previous years allowed the prediction of more than 35000 m3 drainage water/day from the year 2000. This water has particularly high levels of fluorides, which represents a permanent risk for the rural population, which relies on groundwater (wells) for its daily consumption. To minimize adverse health affects and to build on earlier work, the current study was focussed on the sorption performances of coal fly ash in the dynamic mode and on regeneration tests of these ashes for possible revalorization. In this study, we were interested in both the defluoridation of subsoil waters in Youssoufia (drainage waters) by percolation through a column of fly-ash collected from the power station of El Jadida and in fluoride desorption from the ash.The first results from the characterization of this water showed that fluoride concentrations were elevated, exceeding the water quality standard established by the World Health Organization (WHO), 0.7 mg/L for a semi-arid climate. This abnormally elevated content in fluoride comes from the raw phosphates, which have a high fluoride content. Chemical analysis of the fly-ash, carried out by x-ray fluorescence, demonstrated that the principal components were silica, alumina, oxide iron (Fe2O3), and calcium oxide.With respect to the first objective of this study, the sorption experiments of water soluble F- ions from the drainage waters were carried out at 25 °C in a glass column (33 cm high, 2.2 cm in internal diameter) filled with a well-defined mass of fly-ash. The process involved: placing 250 mL of the solution in the higher tank (placed in top of the column) and the flows were adjusted to 4.6, 7.7 and 15.4 mL/h. The concentration of fluorides was measured in the effluent every 24 h, with a fluoride ion selective electrode, pH model Orion SA 520 according to a standardized method (AFNOR, T90-004). Each experiment was carried out twice. The drainage water used had a fluoride content of 2.50 mg/L.With respect to the second objective, the study of the desorption of fluorides from the fly-ash was carried out in a static reactor. The choice was related to chemical desorption with soda, and tests were carried out to evaluate the parameters likely to support desorption (concentration of soda, volume to be used, kinetics of desorption). The method used for desorption consisted of brewing the fly-ash in a basic solution (1g of ashes /100mL of soda) during one hour, at a stirring speed of 300 rpm. The concentration of fluorides was then measured in this solution by a potentiometric method following filtration. The fly-ash was removed and rinsed with distilled water and then re-used for a new sorption. The desorption tests were carried out on fly-ash that had been saturated by contact with the drainage waters from Youssoufia ([F] = 2.5 mg/L, pH=7.86). The sorption stage consisted of putting 10 g of ash in contact with 1 L of the drainage water with a stirring rate of 300 rpm and the tests were carried out at ambient temperature.The results of the defluoridation by percolation through the fly-ash showed that the concentration of fluorides in the effluent decreased to 0 mg/L « < 5 10-7 M », when the flow decreased from 15.4 mL/h (flow 1) to 7.7mL/h (flow 2) to 4.8 mL/h (flow 3), after 96 to 120 hours. Similar results were also obtained by Piekos et al (1998).The first regeneration results were encouraging for several reasons. First of all, the regeneration of support was possible and desorption was very important. This demonstrated that basic media are probably favorable for desorption. In parallel, the kinetics of desorption with soda were very fast and they did not exceed one hour for the various soda solution concentrations tested. Indeed, it was noted that at the end of one hour at least 90% of fluorides were desorbed. The optimum conditions for desorption were 60 min of contact and a soda concentration 6 M.Regenerated ashes were placed again in contact with drainage waters containing fluoride concentrations of 2.50 mg/L. A new sorption of fluorides was noted. This result led us to study the effect of cycle numbers on the adsorption-desorption of fluorides in relation to the effectiveness of regeneration. A histogram of the results demonstrated that the quantities adsorbed and desorbed for the same cycle were practically equal for the eight cycles carried out, thus the effectiveness of ash was practically the same
Marginal bone loss around platform-switched and platform-matched implants following immediate dental implant placement – Systematic Review
Objective
This study aimed to examine marginal bone loss (MBL) around immediately placed platform-switched implants (PS) compared to platform-matched (PM) implants; and to critically appraise the available literature on this topic.
Materials and Methods
Randomized control trials (RCTs), non- randomized control trials (NRCT) and case series of immediate placement platform-switched and platform-matched implant, published in English were included in the study. Two databases, namely Medline and PubMed covering the period between July 1966 and July 2023 were searched. A total of five case series, five RCTs and one NRCT were included in this systematic review by using pre-defined study selection criteria and following the PRISMA protocol. A critical appraisal of the selected studies was completed using standardized appraisal checklists, including CASP tool for critical appraisal of RCTs, the Downs and Black checklist for NRCT, and the CEBMa checklist for case series studies.
Results
Five studies showed a statistically significant difference in MBL (PS: 0.18–0.78 mm, PM 0.51–1.19 mm). The studies featured a small sample size, and substantial methodological variability in patients’ selection criteria, implant and abutment designs, connection types and surgical protocols. A high risk of bias was identified, especially in case series studies.
Conclusion
The use of PS implants in immediate placement protocols can lead to a statistically significant reduction in MBL compared to PM implants. However, the results need to be interpreted with caution, given the numerous confounding variables and clinical heterogeneity existing between the studies
Basaltic Dyke with Specific Volcanogenic Structures and its geomorphic evolution: Unique Geoheritage of the Faroe Islands (North Atlantic Ocean)
Volcanic landforms resulting from Cenozoic volcanism represent the most peculiar features of global geodiversity and provide eminent narratives for geoeducation. Among them, however, relict volcanic forms and site-specific landforms in remote areas have received less attention. In this paper, we provide the first description of unique volcanogenic features (hereinafter referred to as pseudo-hieroglyphs) developed on a summit rock wall at the Sandfelli ridge near the village of GjĂłgv in the N Eysturoy Island (Faroe Islands). The geomorphic evolution of the ridge and rock wall during the Quaternary is described and detailed petrographic analyses of the volcanogenic features are provided. Based on observed petrographical features, we interpret the pseudo-hieroglyphs to probably represent unique examples of chaotic horizontal columnar jointing. Following the geomorphological and petrographic examination of the study site, we analyse current Faroese legislation aiming at nature conservation and use this case to discuss broader implications of geoheritage conservation and geotourism in distant regions.Vulkanická krajina vzniklá kenozoickĂ˝m vulkanismem pĹ™edstavuje nejpodivnÄ›jšà rysy globálnĂ geodiversity a poskytuje vynikajĂcĂ pĹ™ĂbÄ›hy pro geovzdÄ›lávánĂ. MĂ©nÄ› pozornosti se však dostává reliktnĂm vulkanickĂ˝m formám a lokálnĂm tvarĹŻm reliĂ©fu v odlehlĂ˝ch oblastech. V tomto ÄŤlánku pĹ™inášĂme prvnĂ popis unikátnĂch vulkanogennĂch tvarĹŻ (dále jen "pseudo-hieroglyfy"), kterĂ© se vyvĂjely na skalnĂ stÄ›nÄ› vrcholu na hĹ™betÄ› Sandfelli u vesnice GjĂłgv v severnà části ostrova Eysturoy (FaerskĂ© ostrovy). Je popsán geomorfologickĂ˝ vĂ˝voj hĹ™betu a skalnĂ stÄ›ny bÄ›hem kvartĂ©ru a jsou uvedeny podrobnĂ© petrografickĂ© analĂ˝zy vulkanogennĂch vlastnostĂ. Na základÄ› pozorovanĂ˝ch petrografickĂ˝ch rysĹŻ interpretujeme pseudo-hieroglyfy, kterĂ© pravdÄ›podobnÄ› pĹ™edstavujĂ jedineÄŤnĂ© pĹ™Ăklady chaotickĂ© horizontálnĂ sloupcovitĂ© odluÄŤnosti. Po geomorfologickĂ©m a petrografickĂ©m studiu zájmovĂ© lokality analyzujeme souÄŤasnou faerskou legislativu zaměřenou na ochranu pĹ™Ărody a uĹľĂváme tohoto pĹ™Ăkladu k diskusi širšĂch dĹŻsledkĹŻ zachovánĂ a geoturistiky geografickĂ©ho dÄ›dictvĂ ve vzdálenĂ˝ch regionech
The separation and determination of rare earths in phosphate deposits from the north of the kingdom of Saudi Arabia
The use of an ion and cation exchange for the separation of rare earth elements from phosphate rocks were investigated. The cation exchange method was found to be most suitable. Rare earth elements separated in this way were analysed by atomic emission using an inductively coupled plasma. Compromise optimum conditions were found and the combined procedure used for thirty nine phosphate rock samples from Saudi Arabia.. The results obtained were confirmed by internal checks on some samples using standard addition. In general, the recovery of individual rare earth elements is high but these vary from sample to sample depending on the sample composition.The use of an ion and cation exchange for the separation of rare earth elements from phosphate rocks were investigated. The cation exchange method was found to be most suitable. Rare earth elements separated in this way were analysed by atomic emission using an inductively coupled plasma. Compromise optimum conditions were found and the combined procedure used for thirty nine phosphate rock samples from Saudi Arabia.. The results obtained were confirmed by internal checks on some samples using standard addition. In general, the recovery of individual rare earth elements is high but these vary from sample to sample depending on the sample composition
Sensitivity to Volcanic Field Boundary
Volcanic hazard analyses are desirable where there is potential for future volcanic activity to affect a proximal population. This is frequently the case for volcanic fields (regions of distributed volcanism) where low eruption rates, fertile soil, and attractive landscapes draw populations to live close by. Forecasting future activity in volcanic fields almost invariably uses spatial or spatio-temporal point processes with model selection and development based on exploratory analyses of previous eruption data. For identifiability reasons, spatio-temporal processes, and practically also spatial processes, the definition of a spatial region is required to which volcanism is confined. However, due to the complex and predominantly unknown sub-surface processes driving volcanic eruptions, definition of a region based solely on geological information is currently impossible. Thus, the current approach is to fit a shape to the known previous eruption sites. The class of boundary shape is an unavoidable subjective decision taken by the forecaster that is often overlooked during subsequent analysis of results. This study shows the substantial effect that this choice may have on even the simplest exploratory methods for hazard forecasting, illustrated using four commonly used exploratory statistical methods and two very different regions: the Auckland Volcanic Field, New Zealand, and Harrat Rahat, Kingdom of Saudi Arabia. For Harrat Rahat, sensitivity of results to boundary definition is substantial. For the Auckland Volcanic Field, the range of options resulted in similar shapes, nevertheless, some of the statistical tests still showed substantial variation in results. This work highlights the fact that when carrying out any hazard analysis on volcanic fields, it is vital to specify how the volcanic field boundary has been defined, assess the sensitivity of boundary choice, and to carry these assumptions and related uncertainties through to estimates of future activity and hazard analyses
Évolution de la qualité physico-chimique et bactériologique d’un effluent laitier sur un cycle annuel
The chemical-physical and bacteriological quality of an effluent produced by a dairy industry located in El Jadida city (Morocco) was studied during 12 months (March 1998-February 1999). The analyzed parameters are temperature (T), pH, suspended matter (SM), chemical oxygen demand (COD), biological oxygen demand in five days (BOD5), total Kjeldahl nitrogen (TKN-N), ammonia (NH4+-N), nitrates (NO3--N), total phosphorus (TP-P), sodium (Na+), chlorides (Cl-), metals heavy (Fe, Zn, Ni, Cd and Mn), total aerobic flora (TAF), fecal coliforms (FC) and fecal streptococci (FS). The results of the chemical-physical characterization show that the studied effluent assumes a variation more or less important during the same day for flow, temperature, pH, salinity and polluting load. The average annual organic matter concentration is very high (average COD= 6140 mg O2/l ± 10% and average BOD5= 3067 mg O2/l ± 10%), the average annual contents of nitrogen and phosphorus are significant (average TKN-N= 148 mg/l ± 10% and average TPP= 29 mg/l ± 10%). The average annual report COD/BOD5 is equal to 2 indicating the biodegradable character of this effluent. The bacteriological characterization indicates that the analyzed effluent undergoes a significant fecal contamination (FC= 2.33 104 CFU/ml ± 10% and FS= 4.00 104 CFU/ml ± 10%). The ratio FC/FS < 1 proves the animals origin of faecal contamination of dairy efluent. The obtained results reveals that the studied wastewater present a degraded quality, which requires an adequate treatment before rejection in the area or possible re-use and the taken of the preventive measures making it possible to reduce so much pollution in volume and in load.Nous avons, pendant 12 mois consécutifs (mars 1998-février 1999) suivi l’évolution de la qualité physico-chimique et bactériologique d'un effluent de laiterie située dans la ville d'El Jadida (Maroc). Les paramètres analysés sont la température (T), le pH, la matière en suspension (MES), la demande chimique en oxygène (DCO), la demande biologique en oxygène en cinq jours (DBO5), l’azote total Kjeldahl (N-NTK), l’azote ammoniacal (N-NH4+), les nitrates (N-NO3-), le phosphore total (P-PT), le sodium (Na+), les chlorures (Cl-), les métaux lourds (Fe, Zn, Ni, Cd et Mn), la flore mésophile aérobie totale (FMAT), les coliformes fécaux (CF) et les streptocoques fécaux (SF).Les résultats de la caractérisation physico-chimique montrent que l'effluent étudié présente des variations horaires plus ou moins importantes au cours de la même journée pour le débit, la température, le pH, la salinité et la charge polluante. La concentration annuelle moyenne en matière organique est très élevée (DCO moyenne = 6140mg d'O2/l ± 10 % et DBO5 moyenne = 3067 mg d'O2/l ± 10 %), les teneurs annuelles moyennes en azote et en phosphore sont importantes (N-NTK moyen = 148 mg/l ± 10 % et P-PT moyen = 29 mg/l ± 10 %). Le rapport annuel moyen DCO/DBO5 est égal à 2 indiquant le caractère biodégradable de cet effluent. La caractérisation bactériologique indique que l’eau usée analysée subit une contamination fécale importante (CF = 2,33 104 UFC/ml ± 10 % et SF = 4,00 104 UFC/ml ± 10 %). Le rapport CF/SF est inférieur à 1, ce qui témoigne d’une contamination fécale d'origine animale de l'effluent étudié. Il en ressort que cet effluent est de qualité assez dégradée, ce qui nécessite un traitement adéquat avant rejet en milieu récepteur ou éventuelle réutilisation et la prise des mesures préventives permettant de réduire la pollution tant en volume qu’en charge
Accuracy of dental implant placement using chairside computer-aided surgery/computer-aided manufacturing-milled guides compared to three-dimensional printed guides
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